Detailed Description

Identifier Interface.

Todo:: Describe concisely what the functions in this module are about.

Functions
hid_t	H5Iregister (H5I_type_t type, const void *object)
	Registers an object under a type and returns an ID for it. More...

void *	H5Iobject_verify (hid_t id, H5I_type_t type)
	Returns the object referenced by an ID. More...

void *	H5Iremove_verify (hid_t id, H5I_type_t type)
	Removes an ID from its type. More...

H5I_type_t	H5Iget_type (hid_t id)
	Retrieves the type of an object. More...

hid_t	H5Iget_file_id (hid_t id)
	Retrieves an identifier for the file containing the specified object. More...

ssize_t	H5Iget_name (hid_t id, char *name, size_t size)
	Retrieves a name of an object based on the object identifier. More...

int	H5Iinc_ref (hid_t id)
	Increments the reference count for an object. More...

int	H5Idec_ref (hid_t id)
	Decrements the reference count for an object. More...

int	H5Iget_ref (hid_t id)
	Retrieves the reference count for an object. More...

H5I_type_t	H5Iregister_type (size_t hash_size, unsigned reserved, H5I_free_t free_func)
	Creates and returns a new ID type. More...

herr_t	H5Iclear_type (H5I_type_t type, hbool_t force)
	Deletes all identifiers of the given type. More...

herr_t	H5Idestroy_type (H5I_type_t type)
	Removes an identifier type and all identifiers within that type. More...

int	H5Iinc_type_ref (H5I_type_t type)
	Increments the reference count on an ID type. More...

int	H5Idec_type_ref (H5I_type_t type)
	Decrements the reference count on an identifier type. More...

int	H5Iget_type_ref (H5I_type_t type)
	Retrieves the reference count on an ID type. More...

void *	H5Isearch (H5I_type_t type, H5I_search_func_t func, void *key)
	Finds the memory referred to by an ID within the given ID type such that some criterion is satisfied. More...

herr_t	H5Iiterate (H5I_type_t type, H5I_iterate_func_t op, void *op_data)
	Calls a callback for each member of the identifier type specified. More...

herr_t	H5Inmembers (H5I_type_t type, hsize_t *num_members)
	Returns the number of identifiers in a given identifier type. More...

htri_t	H5Itype_exists (H5I_type_t type)
	Determines whether an identifier type is registered. More...

htri_t	H5Iis_valid (hid_t id)
	Determines whether an identifier is valid. More...

Function Documentation

◆ H5Iclear_type()

herr_t H5Iclear_type	(	H5I_type_t	type,
		hbool_t	force
	)

Deletes all identifiers of the given type.

Parameters

[in]	type	Identifier of identifier type which is to be cleared of identifiers
[in]	force	Whether or not to force deletion of all identifiers

Returns: Returns a non-negative value if successful; otherwise returns a negative value.

H5Iclear_type() deletes all identifiers of the type identified by the argument type.

The identifier type's free function is first called on all of these identifiers to free their memory, then they are removed from the type.

If the force flag is set to false, only those identifiers whose reference counts are equal to 1 will be deleted, and all other identifiers will be entirely unchanged. If the force flag is true, all identifiers of this type will be deleted.

◆ H5Idec_ref()

int H5Idec_ref ( hid_t id )

Decrements the reference count for an object.

Parameters

[in] id Object identifier

Returns: Returns a non-negative reference count of the object ID after decrementing it, if successful; otherwise a negative value is returned.

H5Idec_ref() decrements the reference count of the object identified by id.

The reference count for an object ID is attached to the information about an object in memory and has no relation to the number of links to an object on disk.

The reference count for a newly created object will be 1. Reference counts for objects may be explicitly modified with this function or with H5Iinc_ref(). When an object identifier’s reference count reaches zero, the object will be closed. Calling an object identifier’s close function decrements the reference count for the identifier which normally closes the object, but if the reference count for the identifier has been incremented with H5Iinc_ref(), the object will only be closed when the reference count reaches zero with further calls to this function or the object identifier’s close function.

If the object ID was created by a collective parallel call (such as H5Dcreate(), H5Gopen(), etc.), the reference count should be modified by all the processes which have copies of the ID. Generally this means that group, dataset, attribute, file and named datatype IDs should be modified by all the processes and that all other types of IDs are safe to modify by individual processes.

This function is of particular value when an application is maintaining multiple copies of an object ID. The object ID can be incremented when a copy is made. Each copy of the ID can then be safely closed or decremented and the HDF5 object will be closed when the reference count for that that object drops to zero.

Since: 1.6.2

◆ H5Idec_type_ref()

int H5Idec_type_ref ( H5I_type_t type )

Decrements the reference count on an identifier type.

Parameters

[in] type The identifier of the type whose reference count is to be decremented

Returns: Returns the current reference count on success, negative on failure.

H5Idec_type_ref() decrements the reference count on an identifier type. The reference count is used by the library to indicate when an identifier type can be destroyed. If the reference count reaches zero, this function will destroy it.

The type parameter is the identifier for the identifier type whose reference count is to be decremented. This identifier must have been created by a call to H5Iregister_type().

◆ H5Idestroy_type()

herr_t H5Idestroy_type ( H5I_type_t type )

Removes an identifier type and all identifiers within that type.

Parameters

[in] type Identifier of identifier type which is to be destroyed

Returns: Returns a non-negative value if successful; otherwise returns a negative value.

H5Idestroy_type deletes an entire identifier type type. All identifiers of this type are destroyed and no new identifiers of this type can be registered.

The type’s free function is called on all of the identifiers which are deleted by this function, freeing their memory. In addition, all memory used by this type’s hash table is freed.

Since the H5I_type_t values of destroyed identifier types are reused when new types are registered, it is a good idea to set the variable holding the value of the destroyed type to H5I_UNINIT.

◆ H5Iget_file_id()

hid_t H5Iget_file_id ( hid_t id )

Retrieves an identifier for the file containing the specified object.

Parameters

[in] id Object identifier

Returns: Returns a file identifier if successful; otherwise returns H5I_INVALID_HID.

H5Iget_file_id() returns the identifier of the file associated with the object referenced by id.

Note: Note that the HDF5 library permits an application to close a file while objects within the file remain open. If the file containing the object id is still open, H5Iget_file_id() will retrieve the existing file identifier. If there is no existing file identifier for the file, i.e., the file has been closed, H5Iget_file_id() will reopen the file and return a new file identifier. In either case, the file identifier must eventually be released using H5Fclose().

Since: 1.6.3

◆ H5Iget_name()

ssize_t H5Iget_name	(	hid_t	id,
		char *	name,
		size_t	size
	)

Retrieves a name of an object based on the object identifier.

Parameters

[in]	id	Object identifier
[out]	name	A buffer for thename associated with the identifier
[in]	size	The size of the `name` buffer; usually the size of the name in bytes plus 1 for a NULL terminator

Returns: ssize_t

H5Iget_name() retrieves a name for the object identified by id.

Up to size characters of the name are returned in name; additional characters, if any, are not returned to the user application.

If the length of the name, which determines the required value of size, is unknown, a preliminary H5Iget_name() call can be made. The return value of this call will be the size in bytes of the object name. That value, plus 1 for a NULL terminator, is then assigned to size for a second H5Iget_name() call, which will retrieve the actual name.

If the object identified by id is an attribute, as determined via H5Iget_type(), H5Iget_name() retrieves the name of the object to which that attribute is attached. To retrieve the name of the attribute itself, use H5Aget_name().

If there is no name associated with the object identifier or if the name is NULL, H5Iget_name() returns 0 (zero).

Note: Note that an object in an HDF5 file may have multiple paths if there are multiple links pointing to it. This function may return any one of these paths. When possible, H5Iget_name() returns the path with which the object was opened.

Since: 1.6.0

◆ H5Iget_ref()

int H5Iget_ref ( hid_t id )

Retrieves the reference count for an object.

Parameters

[in] id Object identifier

Returns: Returns a non-negative current reference count of the object identifier if successful; otherwise a negative value is returned.

H5Iget_ref() retrieves the reference count of the object identified by id.

The reference count for an object identifier is attached to the information about an object in memory and has no relation to the number of links to an object on disk.

The function H5Iis_valid() is used to determine whether a specific object identifier is valid.

Since: 1.6.2

◆ H5Iget_type()

H5I_type_t H5Iget_type ( hid_t id )

Retrieves the type of an object.

Parameters

[in] id Object identifier

Returns: Returns the object type if successful; otherwise H5I_BADID.

H5Iget_type() retrieves the type of the object identified by id.

Valid types returned by the function are:

H5I_FILE	File
H5I_GROUP	Group
H5I_DATATYPE	Datatype
H5I_DATASPACE	Dataspace
H5I_DATASET	Dataset
H5I_ATTR	Attribute

If no valid type can be determined or the identifier submitted is invalid, the function returns H5I_BADID.

This function is of particular use in determining the type of object closing function (H5Dclose(), H5Gclose(), etc.) to call after a call to H5Rdereference().

Note: Note that this function returns only the type of object that id would identify if it were valid; it does not determine whether id is valid identifier. Validity can be determined with a call to H5Iis_valid().

◆ H5Iget_type_ref()

int H5Iget_type_ref ( H5I_type_t type )

Retrieves the reference count on an ID type.

Parameters

[in] type The identifier of the type whose reference count is to be retieved

Returns: Returns the current reference count on success, negative on failure.

H5Iget_type_ref() retrieves the reference count on an ID type. The reference count is used by the library to indicate when an ID type can be destroyed.

The type parameter is the identifier for the ID type whose reference count is to be retrieved. This identifier must have been created by a call to H5Iregister_type().

◆ H5Iinc_ref()

int H5Iinc_ref ( hid_t id )

Increments the reference count for an object.

Parameters

[in] id Object identifier

Returns: Returns a non-negative reference count of the object ID after incrementing it if successful; otherwise a negative value is returned.

H5Iinc_ref() increments the reference count of the object identified by id.

The reference count for an object ID is attached to the information about an object in memory and has no relation to the number of links to an object on disk.

The reference count for a newly created object will be 1. Reference counts for objects may be explicitly modified with this function or with H5Idec_ref(). When an object ID's reference count reaches zero, the object will be closed. Calling an object ID's close function decrements the reference count for the ID which normally closes the object, but if the reference count for the ID has been incremented with this function, the object will only be closed when the reference count reaches zero with further calls to H5Idec_ref() or the object ID's close function.

If the object ID was created by a collective parallel call (such as H5Dcreate(), H5Gopen(), etc.), the reference count should be modified by all the processes which have copies of the ID. Generally this means that group, dataset, attribute, file and named datatype IDs should be modified by all the processes and that all other types of IDs are safe to modify by individual processes.

This function is of particular value when an application is maintaining multiple copies of an object ID. The object ID can be incremented when a copy is made. Each copy of the ID can then be safely closed or decremented and the HDF5 object will be closed when the reference count for that that object drops to zero.

Since: 1.6.2

◆ H5Iinc_type_ref()

int H5Iinc_type_ref ( H5I_type_t type )

Increments the reference count on an ID type.

Parameters

[in] type The identifier of the type whose reference count is to be incremented

Returns: Returns the current reference count on success, negative on failure.

H5Iinc_type_ref() increments the reference count on an ID type. The reference count is used by the library to indicate when an ID type can be destroyed.

The type parameter is the identifier for the ID type whose reference count is to be incremented. This identifier must have been created by a call to H5Iregister_type().

◆ H5Iis_valid()

htri_t H5Iis_valid ( hid_t id )

Determines whether an identifier is valid.

Parameters

[in] id Object identifier

Returns: Returns zero (false), a positive (true) or a negative (failure) value.

H5Iis_valid() determines whether the identifier id is valid.

Valid identifiers are those that have been obtained by an application and can still be used to access the original target. Examples of invalid identifiers include:

Out of range values: negative, for example
Previously-valid identifiers that have been released: for example, a dataset identifier for which the dataset has been closed

H5Iis_valid() can be used with any type of identifier: object identifier, property list identifier, attribute identifier, error message identifier, etc. When necessary, a call to H5Iget_type() can determine the type of the object that id identifies.

Since: 1.8.3

◆ H5Iiterate()

herr_t H5Iiterate	(	H5I_type_t	type,
		H5I_iterate_func_t	op,
		void *	op_data
	)

Calls a callback for each member of the identifier type specified.

Parameters

[in]	type	The identifier type
[in]	op	The callback function
[in,out]	op_data	The data for the callback function

Returns: The last value returned by op

H5Iiterate() calls the callback function op for each member of the identifier type type. The callback function type for op, H5I_iterate_func_t, is defined in H5Ipublic.h as:

typedef herr_t (*H5I_iterate_func_t)(hid_t id, void *udata);

op takes as parameters the identifier and a pass through of op_data, and returns an herr_t.

A positive return from op will cause the iteration to stop and H5Iiterate() will return the value returned by op. A negative return from op will cause the iteration to stop and H5Iiterate() will return failure. A zero return from op will allow iteration to continue, as long as there are other identifiers remaining in type.

Since: 1.12.0

◆ H5Inmembers()

herr_t H5Inmembers	(	H5I_type_t	type,
		hsize_t *	num_members
	)

Returns the number of identifiers in a given identifier type.

Parameters

[in]	type	The identifier type
[out]	num_members	Number of identifiers of the specified identifier type

Returns: Returns a non-negative value if successful; otherwise returns a negative value.

H5Inmembers() returns the number of identifiers of the identifier type specified in type.

The number of identifiers is returned in num_members. If no identifiers of this type have been registered, the type does not exist, or it has been destroyed, num_members is returned with the value 0.

◆ H5Iobject_verify()

void* H5Iobject_verify	(	hid_t	id,
		H5I_type_t	type
	)

Returns the object referenced by an ID.

Parameters

[in]	id	ID to be dereferenced
[in]	type	The identifier type

Returns: Pointer to the object referenced by id on success, NULL on failure.

H5Iobject_verify() returns a pointer to the memory referenced by id after verifying that id is of type type. This function is analogous to dereferencing a pointer in C with type checking.

Note: H5Iobject_verify() does not change the ID it is called on in any way (as opposed to H5Iremove_verify(), which removes the ID from its type’s hash table).

See also: H5Iregister()

◆ H5Iregister()

hid_t H5Iregister	(	H5I_type_t	type,
		const void *	object
	)

Registers an object under a type and returns an ID for it.

Parameters

[in]	type	The identifier of the type of the new ID
[in]	object	Pointer to object for which a new ID is created

Returns: Returns a object identifier if successful; otherwise returns H5I_INVALID_HID.

H5Iregister() creates and returns a new ID for an object.

The type parameter is the identifier for the ID type to which this new ID will belong. This identifier must have been created by a call to H5Iregister_type().

The object parameter is a pointer to the memory which the new ID will be a reference to. This pointer will be stored by the library and returned via a call to H5Iobject_verify().

◆ H5Iregister_type()

H5I_type_t H5Iregister_type	(	size_t	hash_size,
		unsigned	reserved,
		H5I_free_t	free_func
	)

Creates and returns a new ID type.

Parameters

[in]	hash_size	Minimum hash table size (in entries) used to store IDs for the new type
[in]	reserved	Number of reserved IDs for the new type
[in]	free_func	Function used to deallocate space for a single ID

Returns: Returns the type identifier on success, negative on failure.

H5Iregister_type() allocates space for a new ID type and returns an identifier for it.

The hash_size parameter indicates the minimum size of the hash table used to store IDs in the new type.

The reserved parameter indicates the number of IDs in this new type to be reserved. Reserved IDs are valid IDs which are not associated with any storage within the library.

The free_func parameter is a function pointer to a function which returns an herr_t and accepts a void*. The purpose of this function is to deallocate memory for a single ID. It will be called by H5Iclear_type() and H5Idestroy_type() on each ID. This function is NOT called by H5Iremove_verify(). The void* will be the same pointer which was passed in to the H5Iregister() function. The free_func function should return 0 on success and -1 on failure.

◆ H5Iremove_verify()

void* H5Iremove_verify	(	hid_t	id,
		H5I_type_t	type
	)

Removes an ID from its type.

Parameters

[in]	id	The ID to be removed from its type
[in]	type	The identifier type

Returns: Returns a pointer to the memory referred to by id on success, NULL on failure.

H5Iremove_verify() first ensures that id belongs to type. If so, it removes id from its type and returns the pointer to the memory it referred to. This pointer is the same pointer that was placed in storage by H5Iregister(). If id does not belong to type, then NULL is returned.

The id parameter is the ID which is to be removed from its type.

The type parameter is the identifier for the ID type which id is supposed to belong to. This identifier must have been created by a call to H5Iregister_type().

Note: This function does NOT deallocate the memory that id refers to. The pointer returned by H5Iregister() must be deallocated by the user to avoid memory leaks.

◆ H5Isearch()

void* H5Isearch	(	H5I_type_t	type,
		H5I_search_func_t	func,
		void *	key
	)

Finds the memory referred to by an ID within the given ID type such that some criterion is satisfied.

Parameters

[in]	type	The identifier of the type to be searched
[in]	func	The function defining the search criteria
[in]	key	A key for the search function

Returns: Returns a pointer to the object which satisfies the search function on success, NULL on failure.

H5Isearch() searches through a given ID type to find an object that satisfies the criteria defined by func. If such an object is found, the pointer to the memory containing this object is returned. Otherwise, NULL is returned. To do this, func is called on every member of type type. The first member to satisfy func is returned.

The type parameter is the identifier for the ID type which is to be searched. This identifier must have been created by a call to H5Iregister_type().

The parameter func is a function pointer to a function which takes three parameters. The first parameter is a void* and will be a pointer to the object to be tested. This is the same object that was placed in storage using H5Iregister(). The second parameter is a hid_t and is the ID of the object to be tested. The last parameter is a void*. This is the key parameter and can be used however the user finds helpful, or it can be ignored if it is not needed. func returns 0 if the object it is testing does not pass its criteria. A non-zero value should be returned if the object does pass its criteria. H5I_search_func_t is defined in H5Ipublic.h and is shown below.

typedef int (*H5I_search_func_t)(void *obj, hid_t id, void *key);

The key parameter will be passed to the search function as a parameter. It can be used to further define the search at run-time.

◆ H5Itype_exists()

htri_t H5Itype_exists ( H5I_type_t type )

Determines whether an identifier type is registered.

Parameters

[in] type Identifier type

Returns: Returns zero (false), a positive (true) or a negative (failure) value.

H5Itype_exists() determines whether the given identifier type, type, is registered with the library.

Since: 1.8.0

Detailed Description

Functions

Function Documentation

◆ H5Iclear_type()

◆ H5Idec_ref()

◆ H5Idec_type_ref()

◆ H5Idestroy_type()

◆ H5Iget_file_id()

◆ H5Iget_name()

◆ H5Iget_ref()

◆ H5Iget_type()

◆ H5Iget_type_ref()

◆ H5Iinc_ref()

◆ H5Iinc_type_ref()

◆ H5Iis_valid()

◆ H5Iiterate()

◆ H5Inmembers()

◆ H5Iobject_verify()

◆ H5Iregister()

◆ H5Iregister_type()

◆ H5Iremove_verify()

◆ H5Isearch()

◆ H5Itype_exists()